The invention relates to a method for recycling objects made of thoriated tungsten without separating the radioactive thorium for disposal as radioactive waste.
The invention deals in particular with a method for recycling defective lamp parts formed of thoriated tungsten, for example electrodes of high-pressure discharge lamps, and scrap pieces of thoriated tungsten which are formed during the production of lamps, for example chips and pieces of wire. The method is also suitable for reprocessing waste thoriated tungsten materials from the production of welding electrodes. Without recycling, the thorium containing tungsten would have to be disposed of as radioactive special waste. In the present context, the term thoriated tungsten is understood as meaning tungsten which contains thorium or a thorium compound, usually thorium oxide, as an additive or dopant.
European specification EP 0 889 006 A1 discloses a method for recovering tungsten from objects made of thoriated tungsten. This recovery method involves separating the dopant thorium or thorium oxide from the tungsten which is being recycled, by means of chemical gas-phase transport. The tungsten from which dopants have been removed is suitable for use as a raw material in the manufacture of lamps.
The object of the invention is to provide a simplified method for recycling objects formed of thoriated tungsten, for reuse, and which recycling avoids the need for (expensive) separation and disposal of radioactive thorium.
According to the invention, this object is achieved by a recycling method for objects consisting essentially of thoriated tungsten including the following method steps:
oxidation of the objects consisting essentially of thoriated tungsten to form thorium-containing or thorium-oxide-containing tungsten oxide powder,
homogenization of the tungsten oxide,
chemical reduction of the homogenized tungsten oxide under a hydrogen gas atmosphere to form recycled thoriated tungsten.
A major advantage of this method over the prior art, is that, in the recycling method according to the invention, there is no need to separate the thorium or thorium oxide from the tungsten. This makes the method according to the invention considerably more efficient and inexpensive than the known recycling methods which separate the tungsten from its dopants. The recycled tungsten which has impurities mostly of thorium or thorium oxide and, depending on the source of the material, various small amounts of impurities, which is formed as the end product of the recycling method according to the invention is eminently suitable as a raw material for the production of electrodes for welding equipment. Thoriated tungsten powder formed in the method according to the invention is advantageously processed into rods by pressing and sintering. Wires, preferably for use as electrodes for welding equipment, are advantageously formed from these rods by means of a conventional wire-drawing method. Given a suitable purity of the thoriated tungsten powder obtained by means of the method according to the invention, this material may also be suitable as a raw material for the manufacture of lamp electrodes.